Hi Dave, I am using SuperTech oil from Wal Mart, until I find a good one to use instead. I use this in a chainsaw and trimmer also. I think I figured this out and why I don't get the revs that Scott gets. I now have a WT 324 carb, and I now know from the Walbro info posted on this thread by others and you that it is a 11mm venturi. I visually checked it against my Zama and the Zama is only about 9mm. With a less restrictive muffler and the Toro's ability to draw fuel even without the carb pump working as I accidently proved, (I accidently put the carb spacer on upside down, the pump didn't work, but the engine still ran) I think a too small of a carb is probably not supplying enough air for proper combustion. There is definitely enough fuel. Here is a photo, the Zama is still bolted to the engine and the Wt 324 is besides it. (My problem has probably been a too small carb all along.) Working on too many engines, and projects, at the same time doesn't help either. I sure am using the NGK plug, it is a resistor plug and have you ever tried to find resistor plugs for chainsaw/trimmer engines locally? NonResistor plugs are easy to find but I had to order resistor plugs online.